The present invention relates to a valve actuation (VA) apparatus for an internal combustion engine, and more particularly, to a VA apparatus constructed to adjust the lift of an engine valve to an appropriate amount.
Typically, the VA apparatus, adapted to intake valves as an engine valve, includes: (a) a driving shaft that rotates in synchronism with rotation of a crankshaft, (b) a crank cam that is arranged at the outer periphery of the driving shaft and that has an axis eccentric with an axis of the driving shaft, and (c) a valve operating (VO) cam that receives torque of the crank cam through a transmission mechanism of multi-node linkage and that opens the intake valve against a biasing force of a valve spring by slide contact of a cam face with the top face of a valve lifter arranged at the upper end of the intake valve.
The transmission mechanism includes: (a) a rocker arm that is disposed above the VO cam and that is swingably supported on a control shaft, (b) a crank arm that has one end of circular shape engaged on the outer peripheral surface of the crank cam and another end rotatably coupled to a first arm of the rocker arm through a pin, and (c) a link rod that has a first end rotatably coupled to a second arm of the rocker arm through a pin and a second end rotatably coupled to a cam nose of the VO cam through a pin.
The control shaft is rotatably supported on a bearing disposed at the upper end of a cylinder head. Fixed on the outer peripheral surface of the control shaft is a control cam that has an axis offset with respect to an axis of the control shaft by a predetermined amount; the rocker arm is swingably supported on the outer periphery of the control cam.
In accordance with the engine operating conditions, an actuator, which includes an electric motor and screw transmission means, changes a rotated position of the control cam through the control shaft to vary a rocking fulcrum of the rocker arm, thereby achieving variable control of the lift of the intake valve.
The VO apparatus requires a number of component parts such as transmission mechanism of multi-node linkage. Due to their manufacturing and assembling errors, there often occurs a variation in lift of the intake valve, particularly, variations in valve lift between cylinders.
Therefore, after mounting the component parts to the driving shaft and the control shaft on the cylinder head with the valve spring operated radially, the lift of the intake valve is adjusted by replacing the link rod with another link rod of different length or changing a pivotal point of the link rod and the rocker arm.
However, with adjustment of the valve lift by replacing the link rod, the valve lift is measured with the link rod coupled to the rocker arm or the VO cam. And if a variation in valve lift is produced, the link rod is replaced with another once again. Thus, adjustment requires complicated work, leading to lowering of the efficiency of adjusting work. Moreover, reassemblage of the link rod may cause an assembling error.
On the other hand, with adjustment of the valve lift by changing a pivotal point of the link rod and the rocker arm, a great variation in valve lift is difficult to absorb due to limitation of change in pivotal point.